The present invention relates to tissue products. More particularly, the invention pertains to multi-ply, additive composition treated tissue products and to a method for making the products.
Consumer tissue products such as facial tissue and bath tissue are generally used to absorb body fluids and leave the skin dry. The tissues are predominantly formed of cellulosic paper-making fibers by manufacturing techniques designed specifically to impart softness to the tissue. Despite specific efforts to select fibers and form the tissues with high levels of softness, these consumer tissue products may still have a tendency to abrade the skin.
In an attempt to reduce skin abrasion, additive compositions have been applied to the tissue. The additive compositions, sometimes generally referred to as lotions, function either to provide lubricity causing the tissue to glide across the surface of the skin, or to leave the tissue and be deposited on the skin for a skin health/cosmetic benefit. Additive compositions have been applied to tissues by techniques such as printing or spraying and at levels typically above 1 weight percent to as much as 30 weight percent, based on the weight of the tissue.
In the past, however, various problems have been experienced in constructing tissue products with lotions. For instance, lotions tend to cause multi-ply tissues to deply. It is theorized that ply bonding is impaired because these formulations contain oily, waxy, or both oily and waxy components which hinder bonding between the plies. It appears that the lotion may actually interrupt fiber-to-fiber bonding between the plies. Moreover, it is theorized that conventional mechanical ply bonding processes such as embossing and crimping are inherently ineffective for ply bonding of lotion treated tissues. Specifically, the tackiness of the lotion tends to cause the outer plies of the tissue to stick to the embossing or crimping rolls, thus separating the individual plies from one another as the tissue exits the bonding nip.
A variety of approaches have been employed over the years in an attempt to improve the ply bonding of lotion treated tissues. One approach has been to apply the lotion formulation after the tissue has been ply bonded. While this approach partially improves ply bonding, it continues to have inherent deficiencies because the mechanical forces associated with applying lotion to the tissue may disrupt the previously imparted bonds. Also, it is theorized that the oily and waxy components of the lotion may diminish fiber-to-fiber bonds even when the lotion is applied after the ply bonding operation.
A second approach that has been employed to improve ply bonding in lotion treated tissues has been to adhesively bond the plies together. Adhesive ply bonding, however, represents an added expense and tends to increase the stiffness of the multi-ply tissue.
A third approach to the problem is one disclosed in U.S. Pat. No. 4,513,051 to Lavash entitled xe2x80x9cTissue Paper Productxe2x80x9d and in U.S. Pat. No. 4,481,243 to Allen entitled xe2x80x9cPattern Treated Tissue Paper Productxe2x80x9d which are incorporated herein by reference. These patents disclose a method of treating a multi-ply tissue product with an emollient, where the emollient is distributed over a major portion of each surface except for the area in which the plies are crimped together. An apparent disadvantage with this approach is that a portion of the planar surface area of the tissue is void of the additive composition.
Consequently, a need still remains for a lotion treated tissue having improved ply bonding, as well as a process to provide enhanced ply bonding of multi-ply tissues that have been treated with additive compositions.
The present invention recognizes and addresses the deficiencies and drawbacks of the prior art. Accordingly, it is an object of the present invention to provide an improved additive composition-treated multi-ply tissue product.
Another object of the present invention is to provide a process for bonding at least two tissue plies together in which at least one of the plies has been treated with an additive composition.
Still another object of the present invention is to provide a hot embossing process for bonding additive composition treated tissue plies together.
In response to the above-described deficiencies associated with existing approaches to ply bonding of additive composition treated tissues, a new method for manufacturing multi-ply, additive composition treated tissue has been developed. The method allows for the manufacture of tissue products containing an additive composition and having improved ply adhesion and desirable aesthetic qualities.
Hence, one aspect of the invention relates to a method of making a tissue product. The method comprises the steps of applying an additive composition to a deposition region of at least one of a plurality of tissue plies; forming a bonding nip between a pattern roll and a backing roll, the pattern roll comprising raised bonding elements; heating at least one of the pattern roll and the backing roll to a surface temperature above ambient temperature; and transporting the plurality of tissue plies through the bonding nip such that the bonding elements compress the plurality of tissue plies in at least the deposition region.
The present inventors have discovered that when an additive composition treated tissue web is heated at the right temperature, depending on the additive composition, number of plies and the speed of the web between the embossing rolls, the additive composition melts to a liquid and intermingles with the fiber in the areas of the embossing elements. Once the tissue web exits out of the heated embossing station, the additive composition cools to a solid state with the plies bonded together. Further, adhesion of the tissue plies to the rolls is reduced, and therefore there is less force acting to separate the plies as the tissue sheet exits the bonding nip.
The pattern roll and backing roll may comprise matched steel rolls, wherein the tissue is pressed and pinched between the inter-engaging surfaces in the bonding nip. Alternatively, the backing roll may comprise a smooth steel roll, which is commonly referred to as an anvil roll. Still alternatively, the backing roll may comprise a resilient roll, which is commonly referred to as a rubber coated roll. The use of a resilient roll may be less desirable where the additive composition or the elevated temperature degrades the roll covering or where the tissue tends to adhere to the resilient roll. The pattern roll may comprise an embossing roll, a crimp roll, or other such roll having raised bonding surfaces to compress the tissue plies against the backing roll.
It should be appreciated that the terms xe2x80x9csteel rollxe2x80x9d and xe2x80x9crubber coated rollxe2x80x9d are not specifically limited to rolls formed of steel and rubber, but rather refer to rolls having different relative surface hardnesses.
In particular embodiments, both the pattern roll and the backing roll are heated above ambient temperature. Alternatively, only one of the pattern roll and backing roll may be heated above ambient temperature. Suitable surface temperatures of the rolls may depend on a number of factors, such as the basis weight and fiber composition of the tissue web, the basis weight and formulation of the additive composition, the speed of web travel, and the like. In particular embodiments, the rolls have a surface temperature of at least about 65xc2x0 C., particularly from about 65xc2x0 C. (149xc2x0 F.) to about 104xc2x0 C. (221xc2x0 F.), and more specifically from about 85xc2x0 C. (185xc2x0 F.) to about 95xc2x0 C. (203xc2x0 F.), for improved performance.
The roll or rolls may be heated by any suitable means. In particular applications, for example, a roll may be heated by a circulating supply of heated oil, water, gas, steam or the like. One or both of the rolls could alternatively be internally or externally heated by an electrical heat generating device; infrared, radiant or a conductive heat generating device; or the like. Other objects, features, and aspects of the present invention are discussed in greater detail below.